EP2448875B1 - Glass compositions for joints of devices operating at high temperatures, and assembly method using same - Google Patents

Description

TECHNICAL AREA

The invention relates to glass compositions, and more particularly to glass compositions for apparatus joints operating at high temperatures, for example from 600 to 1000 ° C., in particular from 700 to 900 ° C.

More specifically, the invention relates to glass compositions for joints of a high temperature electrolyser ("EHT" or "HTE" that is to say "High-Temperature Electrolyzer" in English) or a battery high temperature fuel ("SOFC" or "Solid Oxide Fuel Cell" in English language) comprising a stack of elementary cells.

The invention further relates to a method of assembling at least two parts using said glass compositions. These parts include parts that go into the constitution of a high temperature electrolyzer or a high temperature fuel cell ("SOFC" or "Solid Oxide Fuel Cell" in English).

The technical field of the invention can thus be defined in a general way as that of glass joints whose function is to ensure the seal between the different compartments of apparatus in which fluids are conveyed. high temperatures. More particularly, the technical field of the invention is that of the glass seals sealing between the different compartments in which the gases are conveyed and produced in high temperature electrolysers or high temperature fuel cells, especially those comprising a stack. elementary cells which generally operate between 600 and 1000 ° C, in particular between 700 ° C and 900 ° C.

STATE OF THE PRIOR ART

In high temperature electrolysers, the electrolysis of water at high temperature is carried out from vaporized water. The function of a high temperature electrolyser is to transform the water vapor into hydrogen and oxygen according to the following reaction: 2H ₂ O _(g) → 2H ₂ + O ₂ .

This reaction is carried out electrochemically in the cells of the electrolyser.

Each elementary cell is, as shown on the figure 1 , consisting of two electrodes, namely an anode (1) and a cathode (2), sandwiching a solid electrolyte generally in membrane form (3).

The two electrodes (1, 2) are electronic conductors, and the electrolyte (3) is an ionic conductor.

• A la cathode (2), la demi-réaction est la suivante : 2H₂O + 4 e^- → 2H₂ + 2O^2- ;
• Et à l'anode (1), la demi-réaction est la suivante: 2O^2- → O₂ + 4e^-.

The electrochemical reactions are at the interface between each of the electronic conductors and the ionic conductor.

• At the cathode (2), the half-reaction is the following: 2H ₂ O + 4 e ^- → 2H ₂ + 2O ^2- ;
• And at the anode (1), the half-reaction is: 2O ^2- → O ₂ + 4e ^- .

The electrolyte (3), placed between the two electrodes, is the place of migration of O ^2- ions (4), under the effect of the electric field created by the potential difference imposed between the anode (1) and the cathode (2).

An elementary reactor, represented on the figure 2 , consists of an elementary cell (5) as described above, with an anode (1), an electrolyte (3), and a cathode (2) and two mono-polar connectors or more precisely two half-interconnectors (6, 7) which provide electrical, hydraulic and thermal functions. This elementary reactor is called module.

To increase the flow rates of hydrogen and oxygen produced, and as shown on the figure 3 , a plurality of elementary modules are stacked (8), the cells (5) being then separated by interconnectors or bipolar interconnection plates (9).

The set of modules (8) is positioned between two upper (10) and lower (11) interconnection plates which carry power supplies and gas supplies (12). This is called stacking or stacking ( figure 3 ).

• les stacks tubulaires, dans lesquels les cellules sont des tubes, et
• les stacks planaires, dans lesquels les cellules sont fabriquées sous forme de plaques comme sur la figure 3.

There are two concepts, configurations, architectures for stacks:

• tubular stacks, in which the cells are tubes, and
• planar stacks, in which the cells are manufactured in the form of plates as on the figure 3 .

In planar architecture, cells and interconnectors are in contact at many points. The manufacture of the stack, the stack, is subject to fine tolerances as to the flatness of the cells to avoid too high contact pressures and inhomogeneous distribution of stresses, which can lead to cell cracking.

Seals in a stack stack are intended to prevent hydrogen leakage from the cathode to adjacent anodes, to prevent oxygen leakage from the anode to adjacent cathodes, to prevent a hydrogen leak towards the outside of the stack, stack, and finally to limit the leakage of water vapor from the cathodes to the anodes.

As part of the stacking development for high temperature electrolysis ("EHT"), and as shown on the figure 4 , gas-tight seals (13) are thus produced between the planar electrolysis cells (5), each consisting of an Anode / Electrolyte / Cathode ceramic trilayer, and the interconnectors or metal interconnection plates (9).

It should be noted that the dimensions in μm given on the Figure 4 are given only as examples.

More specifically, a seal is formed on the one hand between the lower surface of each cell (5) and the upper half-interconnector (14) of the interconnection plate located below the cell, and on the other hand between the upper surface of each cell and the lower half-interconnector (15) of the interconnection plate located above the cell (5).

These seals (13) should generally have an air leakage rate of less than 10 ^-3 Nml / min / mm between 700 ° C and 900 ° C under a pressure differential of 20 to 500 mbar.

In addition to this sealing function, the seal may, in some cases, have secondary functions of assembly and electrical conduction. For some stack architectures, a ceramic part, called cell support, can be placed between the cells and the interconnectors; and gas-tight seals are then also required with this cell support piece.

Several sealing solutions are currently studied, namely: ceramic elements or adhesives, glass or glass-ceramic seals, compression metal seals, compression mica seals, brazed joints and mixed solutions using several of these techniques.

These seals must make it possible to ensure the seals between the cathode chamber and the outside, between the anodic chamber and the outside, and between the two rooms, and thus avoid gas leaks between the two rooms and to the outside.

As already mentioned above, we are particularly interested here in the glass joints.

The glasses used for these seals can be either simple glass or crystallizable glass also called glass-ceramic, or a mixture of these two glasses, or even simple glass which is added ceramic particles.

Most of the glasses used for these seals are generally in a solid form at the temperature of use, namely generally between 600 ° C. and 1000 ° C., in particular between 700 ° C. and 900 ° C., for example 850 ° C. These seals are called "hard" joints and generally have a viscosity greater than 109 Pa.s at 850 ° C.

The main constraint to be respected in this situation is to formulate a joint having a coefficient of thermal expansion / expansion "CET" or ("Thermal expansion coefficient" or "TEC" in English), adapted to the other elements of the junction, in particular to ceramic and metal parts.

With regard to single glasses, compositions SiO ₂ -CaO-B ₂ O ₃ ; -Al ₂ O ₃ are studied in document [1], BaO-Al ₂ O 3 -SiO ₂ compositions are described in document [2] and in document [3], and finally compositions LiO ₂ -Al ₂ O ₃ -SiO ₂ are mentioned in document [4], but it is difficult with these compositions to achieve CET adapted to the junctions.

The glass-ceramic glasses are, in turn, generally presented as being more chemically and mechanically resistant by controlling the crystallization of the glass using particular nucleating agents and heat treatments.

The parameters to be controlled for these glass-ceramic glasses are the glass formulation and thermal cycles to achieve forming the crystalline phase (s) having the desired properties.

Thus, LAS (LiO ₂ -Al ₂ O; -SiO ₂ ) glass-ceramic compositions are described in document [4], BAS (BaO-Al ₂ O ₃ -SiO ₂ ) compositions are studied. in documents [2] and [6], compositions of the BCAS (Barium Calcium Aluminosilicate) type are mentioned in documents [7] and [8], and finally compositions SiO ₂ -CaO-MgO-Al ₂ O ₃ make the subject of the document [9].

However, the development of formulations and heat treatments for glass-ceramic glasses remains delicate because the junction material changes over time, with the modification of the crystalline phases and because of the creation of interfaces between the materials in contact. The industrial development of this type of glass ceramic remains complex.

Finally, the addition of ceramic particles of different sizes and shapes to simple glasses controls and adjusts the viscosity and TEC of the sealing material [10, 11]. The delicate point lies in the presence of vitreous phase in large quantities that can cause problems of corrosion or evaporation at high temperature.

In addition to the "hard" seals described above, which are in solid form at operating temperature, SrO-La ₂ O ₃ -Al ₂ O ₃ -B ₂ O ₃ -SiO ₂ compositions, which make it possible to obtain a glass fluid at operating temperatures are disclosed in [5]. These compositions make it possible to accommodate the large differences in CET, but the formulations developed in this document are not sufficiently resistant from a mechanical point of view, precisely because of this excessive fluidity of the glass, in order to maintain the tightness faced with the differences in imposed pressures.

Document [12] describes a sodium-sulfur cell which comprises a solid electrolyte tube, an insulating ring that electrically isolates a positive electrode compartment from a negative electrode compartment, and a 100 to 500 μm gap between the solid electrolyte tube and the insulating ring and a glass solder that fills this gap to secure the insulating ring to the electrolyte tube.

To make the assembly between the solid electrolyte tube and the insulating ring, the lower part of the electrolyte tube is inserted into the insulating ring, a glass ring is inserted in the gap formed between the solid electrolyte tube. and the insulating ring, then heat and melt the glass ring in an electric oven.

• 0 à 80 % en poids de SiO₂ ;
• 0 à 30% en poids d'Al₂O₃ ;
• 0 à 80% en poids de B₂O₃ ;
• et 0 à 30% en poids de Na₂O.

The solder glass is an aluminoborosilicate glass, for example comprising the following 4 ingredients in% by weight:

• 0 to 80% by weight of SiO ₂ ;
• 0 to 30% by weight of Al ₂ O ₃ ;
• 0 to 80% by weight of B ₂ O ₃ ;
• and 0 to 30% by weight of Na ₂ O.

In Table 1 of document [12], examples of solder glasses SiO ₂ / Al ₂ O ₃ / B ₂ O ₃ / Na ₂ O are given. It should be noted that the compositions of the glasses of Table 1 are expressed in terms of % in weight.

Note also that the composition E of Table 1 is not standardized to 100 and that, therefore, any comparison with this composition of the document [12] is impossible.

The claimed composition (A) differs from the compositions of this document, particularly as regards the B ₂ O _{3 content} .

In addition, the glasses described in US Patent 5,196,277 [12] are solder glasses for low temperature sealing applications, in contrast to the claimed compositions (A) and (B) which are specifically formulated for high temperature sealing applications and which have properties, particular viscosity but also low reactivity vis-à-vis the materials in contact, suitable for this application.

It follows from the above that there is currently no satisfactory glass composition for use in seals for high temperature equipment such as high temperature electrolysers or batteries. high temperature fuel.

There is therefore a need for a glass composition that gives a chemically and mechanically resistant joint, including mechanical properties allowing it to adapt to CET sometimes very different materials to assemble.

There is also a need for a glass composition that is not subject to corrosion or high temperature evaporation phenomena.

There is still a need for such a glass composition which has little or no interaction with the materials to be assembled.

There is, moreover, a need for a glass composition that can be prepared reliably, easily and reproducibly without, in particular, using complex thermal cycles.

Finally, there is a need for such a glass composition whose properties are stable over time, especially under high temperature conditions.

STATEMENT OF THE INVENTION

The object of the present invention is to provide a glass composition which meets among others the needs listed above.

The object of the present invention is still to provide a glass composition which does not have the drawbacks, defects, limitations and disadvantages of the glass compositions of the prior art and which solves the problems of the compositions of the prior art.

• 72,3% de SiO₂ ;
• 7,8% de B₂O₃ ;
• 14% de Na₂O
• 5,9% de Al₂O₃

ou bien par :

• 7,3% de SiO₂
• 7.8% de B₂O₃
• 12% de Na₂O
• 5,9 % de Al₂O₃

et par une composition de verre (B) constituée en pourcentages molaires par :

• 63 à 76% de SiO₂ ;
• 5 à 12% de ZrO₂ ;
• 0 à 12 % de B₂O₃ ;
• 0 à 2% de La₂O₃ ;
• 11 à 14% de Na₂O ;
• 3 à 5% de K₂O.

This object, and still others, are achieved according to the invention by a glass composition characterized in that it is selected from the group consisting of a glass composition (A) constituted in molar percentages by:

• 72.3% SiO ₂ ;
• 7.8% B ₂ O ₃ ;
• 14% Na ₂ O
• 5.9% Al ₂ O ₃

or by:

• 7.3% SiO ₂
• 7.8% of B ₂ O ₃
• 12% Na ₂ O
• 5.9% Al ₂ O ₃

and by a glass composition (B) constituted in molar percentages by:

• 63 to 76% SiO ₂ ;
• 5 to 12% ZrO ₂ ;
• 0 to 12% of B ₂ O ₃ ;
• 0 to 2% of La ₂ O ₃ ;
• 11 to 14% Na ₂ O;
• 3 to 5% K ₂ O.

It is obvious that the total of the constituents of each of the glass compositions according to the invention is equal to 100% in molar percentages.

The glass compositions according to the invention can be defined as simple glass compositions, that is to say that they comprise little or no crystalline phase, that they only consist of a glassy phase with from their development and above all else (other) heat treatment, all maintenance at a high temperature.

In addition, generally, the glass compositions according to the invention comprise still less than 50% by weight of crystalline phase and preferably 0% by weight of crystalline phase after their maintenance at a temperature of 600 to 1000 ° C., in particular 700 ° C at 900 ° C for a duration greater than 1 hour.

In other words, the glass compositions according to the invention, and the joints comprising these compositions also remain vitreous, that is to say they have little or no crystallization of the glass, after maintaining the seal at temperatures such as the operating temperatures of electrolysers or high temperature fuel cells which are generally from 600 ° C to 1000 ° C, in particular from 700 ° C to 900 ° C, and for example from 800 ° C to 850 ° C, even for long periods, for example up to 1 month or 720 hours.

The compositions according to the invention can thus be defined as "non-devitrifying" compositions, that is to say compositions which remain in their essentially vitreous initial state, even after exposure to high temperatures.

In addition, the compositions according to the invention are such that their viscosity is in the range of 10 ⁷ to 10 ⁸ dPa.s in the range of 700 ° C to 900 ° C, which allows the glass to be in a viscoplastic state giving the joint, on the one hand, a certain flexibility to be able to adapt to the coefficients of thermal expansion of the different materials with which it is in contact, and on the other hand, a satisfactory rigidity to be able to withstand the differences in pressures imposed between the different compartments. Surprisingly, the glass compositions according to the invention thus provide an optimal balance between flexibility and rigidity.

In addition, the compositions according to the invention also have a low level of interaction with the materials with which they are in contact whether they are ceramics such as ceramics type "YSZ", or "MACOR ^® "; metals and alloys such as high chromium steels (Crofer ^® ), high chromium nickel alloys (Haynes ^® 230); or alternatively electrolytes such as the LSM type electrolyte; or Cermets such as Cermet Ni.

The excellent properties of the compositions according to the invention are very stable over time, for periods of up to a month, at high temperature, for example from 600 ° C. to 1000 ° C., and in particular from 700 ° C. to 900 ° C.

The compositions according to the invention are not described in the prior art as represented by the documents cited above, do not present the defects and disadvantages of the compositions of the prior art and provide a solution to the problems of the compositions of the prior art.

The glass transition temperature of the compositions according to the invention is generally lower than the preferred operating temperatures of electrolyzers or high temperature fuel cells which are generally from 700 ° C. to 900 ° C. and, for example, from 800 ° C. to 850 ° C. vs.

Thus, the glass transition temperatures of the compositions (A) are generally from 580 ° C to 620 ° C, while the glass transition temperatures of the compositions (B) are generally from 600 ° C to 680 ° C.

• 66% de SiO₂ ;
• 5,1% de B₂O₃;
• 13,4% de Na₂O ;
• 4, 4 % de K₂O ;
• 10,1% de ZrO₂ ;
• 1% de La₂O₃.

ou bien par :

• 74,9% de SiO₂ ;
• 12,9% de Na₂O ;
• 4,2% de K₂O
• 7% de ZrO₂ ;
• 1% de Lia₂O₃.

Advantageously, the composition "B" is constituted in molar percentages by:

• 66% SiO ₂ ;
• 5.1% B ₂ O ₃ ;
• 13.4% Na ₂ O;
• 4, 4% K ₂ O;
• 10.1% ZrO ₂ ;
• 1% of ₂ O ₃ .

or by:

• 74.9% SiO ₂ ;
• 12.9% Na ₂ O;
• 4.2% K ₂ O
• 7% ZrO ₂ ;
• 1% Lia ₂ O ₃ .

The glass composition according to the invention can be in the form of a powder or in the form of a solid block.

• on met en contact les pièces avec une composition de verre selon l'invention, telle qu'elle a été définie plus haut ;
• on chauffe l'ensemble formé par les pièces et la composition de verre à une température suffisante pour faire fondre la composition de verre afin de former un joint entre les pièces ;
• on refroidit l'assemblage formé par les pièces et le joint.

The invention further relates to a method of assembling at least two parts, wherein the following successive steps are carried out:

• the pieces are brought into contact with a glass composition according to the invention, as defined above;
• the assembly formed by the parts and the glass composition is heated to a temperature sufficient to melt the glass composition to form a seal between the pieces;
• the assembly formed by the parts and the joint is cooled.

According to a first embodiment, the step of contacting the pieces with the glass composition is made by forming a powder of the glass composition, suspending this powder in an organic binder so as to obtain a suspension or paste, and by coating at least one surface of the parts to be assembled with the suspension or paste obtained.

According to a second embodiment, the step of bringing the parts into contact with the glass composition is carried out by preparing a glass piece having the shape of the joint to be formed and then placing this piece between the surfaces of the parts to be assembled. .

Advantageously, said glass piece may be prepared by compacting and sintering a powder of the glass composition in a mold conforming to the shape of the glass piece.

Or, said glass piece may be a block of solid glass prepared by direct casting the molten glass composition into a mold conforming to the shape of the glass piece.

By operating according to this second embodiment of the contacting in particular when said glass piece is a block of solid glass, it has been found that the crystallization inside the seal was almost non-existent and that the seal retained its contents. vitreous characteristics during operation.

Advantageously, the parts to be assembled may be made of a material chosen from metals; metal alloys; ceramics; and the composite materials comprising more than one of the aforesaid materials.

Advantageously, the at least two parts to be assembled may be of different materials.

Advantageously, the at least two parts to be assembled can be parts of a high temperature electrolyser EHT or a high temperature fuel cell SOFC.

The invention further relates to a seal obtainable by the method described above.

The invention also relates to an assembly that can be obtained by the method described in the foregoing.

The invention finally relates to a high temperature electrolyser or a high temperature fuel cell comprising such an assembly.

The invention will be better understood on reading the following detailed description given for illustrative and non-limiting purposes in relation to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

• The figure 1 is a schematic vertical sectional view of an elementary cell of a high temperature electrolyser ("EHT");
• The figure 2 is a schematic view in vertical section of an elementary reactor or elementary module of a high temperature electrolyser ("EHT");
• The figure 3 is a schematic vertical sectional view of a conventional high temperature electrolyser comprising a stack of elementary modules;
• The figure 4 is a schematic vertical sectional view of a basic module of a conventional high temperature electrolyser which shows the seals between the cell and the lower and upper interconnectors;
• The figure 5 is a graph which gives the viscosity as a function of the temperature of two glass compositions (A) according to the invention designated "JV36" (points ●, curve A) and "JV38" (points ▲, curve B), and two glass compositions (B) according to the invention designated "VsC33" (points ◄, curve C) and "VsC34" (points ►, curve D).

• « JV36 » :
  • 72,3% de SiO₂ ;
  • 7,8% de B₂O₃ ;
  • 14% de Na₂O ;
  • 5,9% de Al₂O₃.
• « JV38 » :
  • 74,3% de SiO₂ ;
  • 7,8% de B₂O₃ ;
  • 12% de Na₂O ;
  • 5,9% de Al₂O₃.
• « VsC33 » :
  • 74,9% de SiO₂ ;
  • 12,9% de Na₂O ;
  • 4,2% de K₂O ;
  • 7% de ZrO₂ ;
  • 1% de La₂O₃.
• « VsC34 » :
  • 66% de SiO₂ ;
  • 5,1% de B₂O₃ ;
  • 13,4% de Na₂O ;
  • 4,4% de K₂O ;
  • 10,1% de ZrO₂ ;
  • 1% de Lia₂O₃.

The glasses "JV36", "JV38", VsC33 "and" VsC34 "have the following compositions in molar percentages:

• "JV36":
  • 72.3% SiO ₂ ;
  • 7.8% B ₂ O ₃ ;
  • 14% Na ₂ O;
  • 5.9% Al ₂ O ₃ .
• "JV38":
  • 74.3% SiO ₂ ;
  • 7.8% B ₂ O ₃ ;
  • 12% Na ₂ O;
  • 5.9% Al ₂ O ₃ .
• "VsC33":
  • 74.9% SiO ₂ ;
  • 12.9% Na ₂ O;
  • 4.2% K ₂ O;
  • 7% ZrO ₂ ;
  • 1% of ₂ O ₃ .
• "VsC34":
  • 66% SiO ₂ ;
  • 5.1% B ₂ O ₃ ;
  • 13.4% Na ₂ O;
  • 4.4% K ₂ O;
  • 10.1% ZrO ₂ ;
  • 1% Lia ₂ O ₃ .

• 69,8% de SiO₂ ;
• 7,8% de B₂O₃;
• 12,0% de Na₂O ;
• 4,1% de K₂O ;
• 0,4% de CaO
• 0,2% de BaO.

This graph also shows the viscosity as a function of temperature of a Schott ^® 8422 commercial glass (points ■, curve E) which has the following composition in molar percentages:

• 69.8% SiO ₂ ;
• 7.8% B ₂ O ₃ ;
• 12.0% Na ₂ O;
• 4.1% K ₂ O;
• 0.4% CaO
• 0.2% of BaO.

• La figure 6 présente des photographies prises au microscope électronique à balayage (MEB) de l'interface entre d'une part deux compositions de verre (A) selon l'invention désignées « JV36 » et « JV38 » et un verre commercial Schott^® 8422 et d'autre part des matériaux d'un électrolyseur, après un test sous atmosphère oxydante à la température de fonctionnement (800°C) .
  • La figure 6A est une photographie prise au MEB de l'interface entre le verre « JV36 » selon l'invention et la céramique YSZ après 100 heures de fonctionnement à 800°C. Sur la figure 6A l'échelle en haut à gauche représente 1 µm.
  • Les figures 6B et 6C sont des photographies prises au MEB de l'interface entre le verre « JV38 » selon l'invention et du CROFER^®, après respectivement 100 heures et 720 heures de fonctionnement à 800°C. Sur la figure 6C l'échelle représente 10 µm.
  • Les figures 6D et 6E sont des photographies prises au MEB de l'interface entre le verre Schott^® 8422 et du CROFER^®, après respectivement 100 heures et 720 heures de fonctionnement à 800°C. Sur la figure 6D, l'échelle en haut à gauche représente 1 µm et sur la figure 6E l'échelle représente 10 µm.
  • La figure 6F est une photographie prise au MEB de l'interface entre le verre « JV36 » selon l'invention et un Cermet Ni qui est un électrolyte.
• La figure 7 est une vue schématique du montage de mise en pression pour réaliser des tests d'étanchéité sur les verres selon l'invention et le verre Schott^® 8422.
• La figure 8 est une vue schématique qui montre le détail des emplacements des joints dans le montage de mise en pression de la figure 7.
• La figure 9 est une vue schématique en coupe verticale de l'ensemble du montage utilisé pour réaliser des tests d'étanchéité sur les verres selon l'invention et le verre Schott^® 8422.
• La figure 10 est un graphique qui représente l'enregistrement des chutes de pression lors d'un test de l'anneau fendu réalisé dans les montages des figures 7, 8 et 9.

In ordinate is carried Log η (dPa.s) and in abscissa is carried the temperature T (in ° C).

• The figure 6 shows photographs taken with a scanning electron microscope (SEM) of the interface between on the one hand two glass compositions (A) according to the invention designated "JV36" and "JV38" and a commercial glass Schott ^® 8422 and materials from an electrolyser, after a test under oxidizing atmosphere at operating temperature (800 ° C).
  • The Figure 6A is a photograph taken at SEM of the interface between the "JV36" glass according to the invention and the YSZ ceramic after 100 hours of operation at 800 ° C. On the Figure 6A the scale on the top left represents 1 μm.
  • The Figures 6B and 6C are photographs taken at the SEM of the interface between the "JV38" glass according to the invention and CROFER ^® , after respectively 100 hours and 720 hours of operation at 800 ° C. On the Figure 6C the scale represents 10 μm.
  • The Figures 6D and 6E are photographs taken at the SEM of the interface between Schott ^® 8422 glass and CROFER ^® , after respectively 100 hours and 720 hours of operation at 800 ° C. On the Figure 6D , the scale on the top left represents 1 μm and on the figure 6E the scale represents 10 μm.
  • The figure 6F is a photograph taken at SEM of the interface between the glass "JV36" according to the invention and a Cermet Ni which is an electrolyte.
• The figure 7 is a schematic view of the pressurizing assembly for performing leak tests on the glasses according to the invention and Schott ^® 8422 glass.
• The figure 8 is a schematic view showing the details of the locations of the seals in the pressurizing assembly of the figure 7 .
• The figure 9 is a schematic view in vertical section of the assembly used for carry out leak tests on the glasses according to the invention and Schott ^® 8422 glass.
• The figure 10 is a graph that represents the recording of pressure drops during a test of the split ring made in the assemblies of figures 7 , 8 and 9 .

The abscissa is the time (hours) and the ordinate is the temperature (left in ° C) and the pressure (right in bars).

• La figure 11 présente des photographies, prises au microscope électronique à balayage d'un joint préparé avec une barbotine du verre « JV38 » selon l'invention, après un traitement thermique à 800°C pendant une durée de 100 heures (Figure 11A) ou pendant une durée de 1 mois (Figure 11B) .
• La figure 12 est une photographie, prise au microscope électronique à balayage d'un joint sous forme massive préparé par coulée directe à partir d'un bloc du verre « JV38 » selon l'invention, après un traitement thermique à 800°C pendant un mois.
• La figure 13 est un graphique qui présente les diagrammes DRX d'un joint préparé à partir d'une barbotine de verre « JV38 » selon l'invention, traité à 800°C pendant 100 heures (courbe A), ou traité à 800°C pendant un mois (courbe D) ; du verre « JV38 » brut initial (courbe B), d'un joint sous forme massive préparé par coulée directe à partir d'un bloc du verre « JV38 » selon l'invention, traité à 800°C pendant 100 heures (courbe C), ou traité à 800°C pendant un mois (courbe E).

Curve A represents the pressure (in bars), the straight lines B and C represent respectively the ambient temperature (in ° C) and the temperature of the assembly (in ° C).

• The figure 11 presents photographs, taken under a scanning electron microscope of a joint prepared with a "JV38" glass slip according to the invention, after a heat treatment at 800 ° C. for a duration of 100 hours ( Figure 11A ) or for a period of 1 month ( Figure 11B ).
• The figure 12 is a photograph, taken under a scanning electron microscope of a solid form gasket prepared by direct casting from a block of glass "JV38" according to the invention, after heat treatment at 800 ° C for one month.
• The figure 13 is a graph which presents the DRX diagrams of a joint prepared from a "JV38" glass slip according to the invention, treated at 800 ° C. for 100 hours (curve A), or treated at 800 ° C. for a period of month (curve D); original "JV38" raw glass (curve B), a joint in massive form prepared by direct casting from a glass block "JV38" according to the invention, treated at 800 ° C for 100 hours (curve C), or treated at 800 ° C for one month (curve E).

• La figure 14 est un schéma qui montre le protocole de mise en forme d'un joint par coulée directe dans une préforme de gorge de joint.
  • La figure 14A illustre l'opération de coulée et la figure 14B est une vue de dessous de la préforme de gorge de joint.

The abscissa is 2θ and the ordinate is the number of strokes.

• The figure 14 is a diagram that shows the protocol for shaping a seal by direct pouring into a joint groove preform.
  • The figure 14A illustrates the casting operation and the Figure 14B is a bottom view of the joint groove preform.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The first step of the process according to the invention consists, firstly generally, in preparing and developing a glass composition.

The glass composition according to the invention consists of either silica (SiO ₂ ), boric anhydride (B ₂ O ₃ ), Alumina (Al ₂ O ₃ ), and Na ₂ O (Composition of glass A), or with silica-(SiO ₂ ), zirconium oxide (ZrO ₂ ), boric anhydride (B ₂ O ₃ ), lanthanum oxide (La ₂ O ₃₎ ), Na ₂ O, and K ₂ O (Glass composition B). The preferred molar proportions and molar proportions of each of the components in these compositions A and B have been mentioned above.

According to a first embodiment, the glass composition according to the invention is a pulverulent composition which can be prepared in synthesizing, firstly, from the different pure oxides and / or compounds consisting of several of these oxides a glass containing these oxides.

An example of such a compound consisting of several oxides is mullite, which is the compound 3Al ₂ O ₃ -2SiO ₂ .

These pure or compound oxides are generally in the form of powders. They are weighed in the proportions desired in the final glass composition that is desired, and then they are mixed and milled in any suitable apparatus, such as a mortar.

The mixture of crushed powders is then introduced into a crucible, generally platinum, and the various constituents of the powder mixture are melted by subjecting them, for example, to a stage of 2 hours in air at 1500 ° C. or 1600 ° C. according to the composition of the glass. After cooling, a homogeneous glass is obtained, the glass transition temperature of which generally varies between 540 ° C. and 680 ° C., depending on its composition.

The glass obtained is recovered and then ground in a mortar or other suitable device to obtain a powder of adequate particle size whose grains have a dimension, for example a diameter, for example from 5 to 250 microns, preferably from 10 to 100 μm, in particular 63 μm.

The ground glass is then conventionally mixed with a liquid organic cement or binder that is generally both viscous and sticky in order to obtain a so-called "slip" glass paste. allowing a homogeneous spreading on the surfaces of the substrates to be assembled, between which must be made a tight seal.

In other words, the mixture of glass and binder generally has the consistency of a malleable paste easy to distribute in the often narrow grooves where the joints must be housed.

The binder generally comprises one or more binder compounds such as terpineol or polyvinyl butyral and one or more solvents such as ethanol.

The suspension, paste of the glass composition described above, is spread out, coated, applied, preferably homogeneously on the surface of at least one of the parts to be assembled, and the surfaces of the two parts to be joined are brought into contact. . This brazing configuration is called "sandwich configuration" because the paste of the solder composition is placed directly between the surfaces of the parts to be assembled.

The quantity of paste, suspension of solder composition to be used in this configuration is generally of the order of 0.1 to 0.4 cm ³ of paste per cm ² .

Or, the surfaces of the parts to be joined are brought together so as to leave an interval generally of 1 to 500 μm which will be filled by capillary action by the solder composition, the latter being disposed near the gap to be filled in a space or tank provided for this purpose, said tank being able to have dimensions millimeters according to the knowledge of the skilled person in this field.

This soldering configuration is called "capillary configuration". With the solder compositions according to the invention, it is possible to perform such a capillary brazing, namely an infiltration of the solder into the solder joint, without directly disposing the solder composition between the parts to be assembled, as in the case of the "sandwich configuration".

The quantity of paste, suspension of solder composition to be used in this capillary configuration is generally of the same order as that indicated above.

Or, the glass powder obtained as described above can be compacted and then sintered in a mold or preform, for example graphite, of suitable shape corresponding to the shape of the seal that is desired. This mold or this preform may for example comprise a groove or groove whose shape is that of the groove in which the seal will have to adapt. This produces a sintered glass piece which is removed from the mold and which is then placed between the parts to be assembled.

The glass composition according to the invention may be in the form of not a powder, but a solid block.

It should be noted that a powder generally consists of discrete particles whose size, for example the average diameter can range from 5 μm to 250 μm, whereas a massive block generally has size defined by its largest dimension from 1 to 50 cm.

This massive block can be melted and the molten glass poured directly into a mold or preform, for example graphite, of suitable shape corresponding to the shape of the joint that is desired. This mold or this preform may for example comprise a groove or groove whose shape is that of the groove in which the seal will have to adapt. This produces a piece of glass in the form of a block of solid glass which is removed from the mold and which is then placed between the parts to be assembled.

The preparation, forming a joint in massive form, namely in the form of a glass block, raw casting, is described on the Figure 14 .

A molten glass (141) having a composition according to the invention and contained in a crucible (142), is cast (143) directly into a graphite groove preform (144) ( Figure 14A ).

The Figure 14B is a bottom view of the preform shown in perspective on the figure 14A . The seal groove presented is circular, but other shapes could be envisaged.

Embodiments in which are placed between the parts to be assembled a glass part prepared from sintered compacted glass or a piece of bulk solid glass cast are particularly advantageous because they allow to limit the crystallization phenomenon favored by the use of seals prepared from powders and which occurs during the maintenance of this seal at high temperatures, for example from 700 ° C to 900 ° C, and thus to preserve the essentially vitreous nature of the seal at these high temperatures .

The second step of the method according to the invention generally consists in producing the actual assembly.

Prior to the assembly, and generally before the coating of the surfaces to be assembled by a paste of the glass composition, or prior to the introduction of a sintered compacted glass piece or solid glass both (or more) surfaces of the parts to be assembled are generally degreased in an organic solvent for example of the ketone type, ester, ether, alcohol, or a mixture thereof; then dried.

The parts to be assembled are generally two in number, but it is also possible to assemble simultaneously a larger number of pieces up to 100.

According to the invention, it is possible to assemble, with each time excellent results geometry pieces, complex shape and / or large.

The two or more pieces to be assembled may be of the same material, or they may be of different materials. This is one of the advantages of the composition according to the invention to allow the assembly of very different materials, especially of materials whose thermal expansion coefficients are very different.

The parts to be assembled may be made of a material chosen from metals and alloys such as steels and nickel alloys; Cermets; ceramics; and composite materials comprising a plurality of the aforesaid materials.

The preferred application of the glass compositions according to the invention is the assembly of the various elements constituting an "EHT" or "SOFC" and the materials that can be assembled by the method according to the invention by setting The composition according to the invention will preferably be chosen from the materials that constitute the various elements of these devices.

Thus, the preferred materials for the cathode "EHT" (anode in "SOFC" mode) and the "EHT" anode (cathode in "SOFC" mode) are, respectively, the Cermet Gadolinié nickel-oxide oxide cermet (NiO). -CGO) and strontied Lanthanum Manganite ( _1-x Sr _x Mn _y O _{3 -δ} or LSM).

These are the most common materials currently used industrially in "SOFC" mode, but many other materials and combinations can be envisaged, such as the cermet NiO-YSZ, the nickelates (La ₄ Ni ₃ O ₁₀ , La Nd ₂ NiO ₄ ), chromo-manganites (LaCeSrCrMnO), ferrites (La _1-X Sr _X Fe _Y O _3-δ ), cobaltites ((La _1-X Sr _X Co _Y O _3-δ ) or titanates (La ₄ Sr _n-4 Ti _n O _{3n + 2-δ} ).

Parts ready to be assembled are then placed in a heating device such as than an oven or subjected to heating by any other suitable means.

The assembly can be performed under an air atmosphere.

The parts to be assembled are subjected for example in the furnace to a heating thermal cycle, generally under an air atmosphere.

Thus the assembly formed by the parts and the glass composition (paste, sintered compacted part or massive part) can be brought to the brazing temperature (soldering bearing) by observing a temperature rise preferably "slow", with one or more temperature ramps from room temperature.

This rise in temperature can be done for example with a temperature ramp at a rate of 0.5 ° C per minute.

The soldering bearing is generally carried out at a temperature corresponding to a softening state of the glass, where its viscosity is of the order of 10 ⁵ dPa.s, but this temperature is preferably a temperature at least greater than 300 ° C. at the glass transition temperature.

This so-called "brazing" temperature is a temperature which is a sufficient temperature allowing the formation of the seal with the interfaces, that is to say the wetting of the molten glass composition on the surfaces of the materials constituting the parts to be assembled.

Depending on the compositions, the brazing temperature will therefore vary, for example, from 850 ° C to 1000 ° C.

Such a melting temperature of the compositions allows, according to another advantage of the process of the invention, a use of the assembly, in particular in air for example up to 800 ° C and even up to 900 ° C.

The duration of the brazing, that is to say the thermal cycle of realization of the assembly is generally from 1 to 10 hours.

At the end of the brazing cycle, following the brazing stage, the assembly is cooled to the temperature of use, that is 700 ° C. to 900 ° C., for example 0.5 ° C per minute.

During cooling, the glass composition solidifies and a solid seal is formed.

The assemblies of parts comprising seals prepared by the process according to the invention make it possible to produce structures, apparatus and components of complex shapes having high operating temperatures that can generally range up to 900 ° C. with high precision.

In other words, the method according to the invention can especially be applied to the manufacture of any device, apparatus, structure, component, requiring an assembly between at least two substrates, parts guaranteeing both good mechanical strength and a satisfactory seal at the assembly.

These devices, devices, structures, components can meet needs in different fields but the preferred domain to which Applies the invention is that of electrolysers and high temperature fuel cells.

The invention will now be described by means of the following examples given of course by way of illustration and not limitation.

EXAMPLES

• « JV36 » :
  • 72,3% de SiO₂ ;
  • 7,8% de B₂O₃ ;
  • 14% de Na₂O ;
  • 5, 9% de Al₂O₃.
• « JV38 » :
  • 74,3% de SiO₂ ;
  • 7,8% de B₂O₃ ;
  • 12% de Na₂O ;
  • 5,9% de Al₂O₃ ;

et éventuellement de deux compositions de verre (B) selon l'invention appartenant à la famille « SiO₂-ZrO₂-B₂O₃-La₂O₃-Na₂O-K₂O » dénommées « VsC33 » et « VsC34 » qui présentent respectivement les compositions en pourcentages molaires suivantes :

• « VsC33 » :
  • 74,9% de SiO₂ ;
  • 12,9% de Na₂O ;
  • 4 , 2 % de K₂O ;
  • 7% de ZrO₂ ;
  • 1% de La₂O₃.
• « VsC34 » :
  • 66% de SiO₂ ;
  • 5,1% de B₂O₃;
  • 13,4% de Na₂O ;
  • 4,4% de K₂O;
  • 10,1% de ZrO₂ ;
  • 1% de Lia₂O₃.

In Examples 1 to 3 which follow, the characteristics of two glass compositions (A) according to the invention belonging to the family "SiO ₂ -B ₂ O ₃ -Al ₂ O; -Na ₂ O", designated " JV36 "and" JV38 "which respectively exhibit the compositions in molar percentages as follows:

• "JV36":
  • 72.3% SiO ₂ ;
  • 7.8% B ₂ O ₃ ;
  • 14% Na ₂ O;
  • 5.9% Al ₂ O ₃ .
• "JV38":
  • 74.3% SiO ₂ ;
  • 7.8% B ₂ O ₃ ;
  • 12% Na ₂ O;
  • 5.9% Al ₂ O ₃ ;

and optionally two glass compositions (B) according to the invention belonging to the family "SiO ₂ -ZrO ₂ -B ₂ O ₃ -La ₂ O ₃ -Na ₂ OK ₂ O" designated "VsC33" and "VsC34" which respectively present the compositions in molar percentages as follows:

• "VsC33":
  • 74.9% SiO ₂ ;
  • 12.9% Na ₂ O;
  • 4, 2% K ₂ O;
  • 7% ZrO ₂ ;
  • 1% of ₂ O ₃ .
• "VsC34":
  • 66% SiO ₂ ;
  • 5.1% B ₂ O ₃ ;
  • 13.4% Na ₂ O;
  • 4.4% K ₂ O;
  • 10.1% ZrO ₂ ;
  • 1% Lia ₂ O ₃ .

• 69,8% de SiO₂ ;
• 7,8% de B₂O₃ ;
• 12,0% de Na₂O ;
• 4,1% de K₂O ;
• 0,4% de CaO
• 0,2% de BaO.

And these characteristics are compared to those of Schott ^® 8422 commercial glass, which has the following composition in molar percentages:

• 69.8% SiO ₂ ;
• 7.8% B ₂ O ₃ ;
• 12.0% Na ₂ O;
• 4.1% K ₂ O;
• 0.4% CaO
• 0.2% of BaO.

Example 1

In this example, viscosity measurements are carried out for the two glasses (A) according to the invention described above, called "JV36" and "JV38" and for the two glasses (B) according to the invention described below. , called "VsC33" and "VsC34" and for the comparative glass Schott ^® 8422.

These measurements were made in two temperature ranges (550 ° C-700 ° C) and (1000 ° C-1500 ° C) that have been correlated by a VFT type law $\left(\mathrm{log\eta }=\mathrm{AT}+\frac{B}{T-{\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="imgf0003.png,imgf0008.png"\; state="\{\{state\}\}">T</figure-callout>}}_0}\right)\mathrm{.}$

We note on the figure 5 on which the plastic, viscous and melted areas of glass have been represented, only in the range of 700 ° C to 850 ° C which constitutes an operating range commonly used in appliances such as high temperature electrolysers or high fuel cells temperature, the "JV36" and "JV38" glasses according to the invention have a viscoplastic behavior giving the joint an optimal combination of flexibility and rigidity.

This is also the case of the VsC33 and VsC34 glasses.

In particular, at 800 ° C., the viscosity of the "JV36" and "JV38" glasses according to the invention is between 10 ⁷ and 10 ⁸ dPa.s.

Example 2

In this example, the interactions of the glass compositions according to the invention is studied and Schott ^® 8422 glass with various materials constituting an electrolyser operating temperature, namely 800 ° C, and for a period of 100 hours in an oxidizing atmosphere .

These tests are conducted in the laboratory with samples of materials representative of the electrolyser, on which there is a small quantity of glass paste implemented in the same way as for the tests on the prototypes. electrolysers. The glass / metal and glass / ceramic samples are treated under air in a muffle oven.

• Étude de l'Interaction du verre « JV36 » avec la céramique « YSZ » pendant 100 heures à 800°C sous une atmosphère oxydante.

The interface is then observed with a scanning electron microscope (SEM).

• Study of the interaction of glass "JV36" with ceramic "YSZ" for 100 hours at 800 ° C under an oxidizing atmosphere.

The Figure 6A is a photograph taken at SEM of the interface between the "JV36" glass according to the invention and the YSZ ceramic after 100 hours of operation at 800 ° C.

• Étude de l'Interaction du verre « JV36 » avec le CROFER^® pendant respectivement 100 heures et 720 heures à 800°C, sous une atmosphère oxydante.

It can be seen that no intermediate phase is observed at the interface.

• Study of the interaction of glass "JV36" with the CROFER ^® for 100 hours and 720 hours respectively at 800 ° C under an oxidizing atmosphere.

The Figures 6B and 6C are photographs taken at the SEM of the interface between the "JV38" glass according to the invention and CROFER ^® , after respectively 100 hours and 720 hours of operation at 800 ° C.

• Étude de l'Interaction du verre Schott^® 8422 avec le CROFER^® pendant respectivement 100 heures et 720 heures à 800°C, sous une atmosphère oxydante.

We see on Figures 6B and 6C that the thicknesses of chromium oxide formed at the interface are respectively 0.75 μm (for 100 hours) and 2 μm (for 720 hours).

• Study of the interaction of Schott ^® 8422 glass with CROFER ^® for 100 hours and 720 hours at 800 ° C under an oxidizing atmosphere respectively.

The Figures 6D and 6E are photographs taken at the SEM of the interface between Schott ^® 8422 glass and CROFER ^® , after respectively 100 hours and 720 hours of operation at 800 ° C.

It is seen in these figures that the chromium oxide thicknesses formed at the interface Schott ^® 8422 / Crofer ^® that are 4 microns respectively (for 100 hours) and 15 microns (for 720 hours) are much larger than those at the glass interface "JV38" according to the invention / Crofer ^®.

The Figure 6F is a photograph taken at SEM of the interface between the glass "JV36" according to the invention and a Cermet Ni which is an electrolyte.

This photograph shows that the glass according to the invention penetrates into all the porosities of this Cermet Ni without any damage.

This example demonstrates that the interactions between the glasses according to the invention and various high temperature electrolyser materials are much less than the interactions between Schott ^® glass and these same materials.

Example 3

In this example, leak tests are carried out by measuring the pressure drop on Schott ^® 8422 glass and on the "JV36" glass according to the invention.

The pressurizing assembly used for these measurements is schematized on the Figure 7 .

• une sole métallique (71) par exemple en acier ;
• un disque ou sole céramique (72) simulant la cellule ;
• une cloche métallique (73).

The assembly consists essentially of 3 parts:

• a metal sole (71) for example of steel;
• a ceramic disc or sole (72) simulating the cell;
• a metal bell (73).

As can be seen on the figure 8 , the test joint is the inner seal (74), deposited in the groove formed by a portion of the metal sole and the blank (75) of the ceramic disc. The so-called servitude joint (76) serves to seal the upper part of the assembly and the pressurization for the leaktightness test of the internal seal (74).

The assembly of the figure 7 is disposed in a pressurizing circuit supplied by an argon circuit (77) comprising adjustment (78), purge (79), and isolation (80) valves, and a sensor (81) (see FIG. figure 9 ).

• Mise en place des joints : les joints, sous forme de pâte, sont mis en place dans les gorges à l'aide d'une seringue sur une hauteur d'environ 2,5 mm (soit environ 0,3 cm³ de pâte par cm² pour le joint interne, et environ 0,2 cm³ de pâte par cm² pour le joint de servitude) ;
• Conditionnement des joints : un traitement thermique préliminaire est appliqué pour former les joints (0,5°C par minute jusqu'à la température de formation T_formation (entre 850°C et 1000°C), pendant 1 à 10 heures puis redescente à 0,5°C par minute) ;
• Mise en place du montage : mise en place de la cloche et des masses sur la maquette dont le poids varie en fonction du niveau de surpression à tester (typiquement entre 60 kg et 150 kg pour une mise en pression de 0,2 bar à 3 bar) ;
• Mise en température du montage : montée à raison de 0,5°C par minute jusqu'à la température de test T_test (750°C à 1000°C) ;
• Mise en pression du montage en montant la pression par paliers de 50 mbar jusqu'à P_test, isolement du circuit et mesure de la chute de pression à l'aide du capteur de pression. Maintien de la pression à P_test tout d'abord pendant une heure puis si l'étanchéité est bonne pendant environ une semaine et enregistrement de la chute de pression (Figure 10) ;
• Refroidissement jusqu'à la température ambiante à raison de 0,5°C par minute.

The procedure of the leak test is as follows:

• Placement of the joints: the joints, in the form of paste, are put in place in the grooves with the aid of a syringe on a height of about 2.5 mm (or about 0.3 cm ³ of paste by cm ² for the inner seal, and about 0.2 cm ³ of dough per cm ² for the service joint);
• Conditioning of the joints: a preliminary heat treatment is applied to form the joints (0.5 ° C per minute up to the formation temperature T _formation (between 850 ° C and 1000 ° C), for 1 to 10 hours then down to 0.5 ° C per minute);
• Setting up of the assembly: installation of the bell and the masses on the model whose weight varies according to the level of pressure to be tested (typically between 60 kg and 150 kg for a pressurization of 0.2 bar to 3 bar);
• Heating of the assembly: mounted at a rate of 0.5 ° C per minute up to the test T _test temperature (750 ° C to 1000 ° C);
• Pressurization of the assembly by mounting the pressure in increments of 50 mbar up to P _test , isolating the circuit and measuring the pressure drop using the pressure sensor. Maintain the pressure at P _test first for one hour then if the seal is good for about a week and record the pressure drop ( Figure 10 );
• Cooling to room temperature at 0.5 ° C per minute.

On the Figure 10 As regards the test of the split ring made with glass "JV36", the leak test is carried out at the nominal temperature (T mounting) of 800 ° C: the circuit is pressurized in increments of 50 mbar (50 mbar, 100 mbar, 150 mbar, 200 mbar, 250 mbar and 300 mbar), with delivery to the P _atm between each setpoint. The circuit is maintained at the pressure of each bearing for 1 hour during which the pressure drop is measured. For the last stage (300 mbar pressure P _test ) and as specified above, we first start by maintaining the circuit for one hour at this pressure, then if the seal is good it is maintained at this pressure (P _test ) for a week during which the pressure drop is measured.

Leakage rates of 10 ^-5 Pa.m ³ .s ^-1 at 800 ° C. under 300 mbar pressure and for 166 hours were measured with the "JV36" glass gasket according to the invention.

With the Schott ^® 8422 glass seal, the best seal measured at the same temperature is only 2.10 ^-3 Pa.m ³ .s ^-1 , under 150 mbar.

Example 4

In this example, the conventionally shaped glass joint properties are compared from a glass paste of the "JV 38" glass or solid seals shaped by direct casting of the same "JV38" glass according to the protocol described on the figure 14A . The tests are conducted in the laboratory in the same manner as in Example 2.

The "conventional" form of the glass joint is used, consisting of the preparation of a so-called "slip" glass paste composed of crushed glass with a particle size ranging from 0 to 63 μm and a mixture of different organic binders.

The mass proportions used are 12% Terpineol, 6% Poly Vinyl Butyral, 12% Ethanol and 70% glass powder.

With this paste, the assembly was made in the following manner: the glass paste is deposited on the following substrates: stainless steel Crofer ^® , Haynes ^® 230 alloy, YSZ or Macor ^® ceramics, and the whole is then heated up to temperature (800 ° C or 900 ° C) with a rise ramp of 0.5 ° C per minute and then slowly cool to 0.5 ° C per minute.

When tested for a hundred hours at 800 ° C, the seal prepared from the preparation "paste", glass slip "JV38" crystallizes little ( Figure 11A ), however, after one month of maintenance at 800 ° C, the joint develops a crystallized phase of albite (Na (Si ₃ Al) O ₈ ) at more than 50% of the volume which is clearly identified on the Figure 11B . The properties of the joint are then completely modified.

To overcome this problem, the joint is shaped in massive form according to the protocol described on the Figure 14A . The seal is constituted by a glass block "JV38", raw casting.

After treatment of this massive seal at 800 ° C for 1 month, the crystallization is virtually non-existent and the seal retains its glass characteristics during operation.

On the Figure 12 , on the contrary, we find Figure 11B the total absence of crystals in the joint.

Examination of the X-ray diffraction patterns of the Figure 13 confirms observations made with a scanning electron microscope.

We note in particular on the Figure 13 that the DRX diagram of the joint prepared from a glass slip treated for one month at 800 ° C shows the characteristic peaks of the crystallization of a phase NaSi ₃ AlO ₈ . The diagrams of the initial raw glass and the joints constituted by a block of solid glass prepared by direct casting, treated 100 hours or 1 month at 800 ° C do not have such peaks, which shows that the joints retain their initial vitreous characteristics and do not crystallize even after prolonged treatment at a high temperature.

REFERENCES

• [1] Zheng R. et al., Journal of Power Sources, 128 (2004), 165-172 .
• [2] Eichler K. et al., Journal of the European Ceramic Society, 19 (1999), 1101-1104 .
• [3] Loehman R. et al., Brow R. "Engineered Glass Composites for Sealing Solid Oxide Fuel Cells" SECA Core Technology Program Review, May 11-13, 2004 Boston, USA .
• [4] US Patent 4,921,738 .
• [5] WO-A1-96 / 05626 .
• [6] US B1-6,430,966 .
• [7] Yang Z. et al., Solid State Ionics 160 (2003), 213-225 .
• [8] Lahl N et al., Journal of Material Sciences, 35 (2000), 3089-3096 .
• [9] WO-A1-99 / 54131 .
• [10] WO-A1-2006 / 069753 .
• [11] US B2-6,828,263 .
• [12] US Patent 5,196,277 .

Claims (18)

1. A glass composition characterized in that it is selected from the group consisting of a glass composition (A) consisting of, in molar percentages:

   - 72.3% of SiO₂;

   - 7.8% of B₂O₃;

   - 14% of Na₂O;

   - 5.9% of Al₂O₃;

   or else by:

   - 74.3% of SiO₂;

   - 7.8% of B₂O₃;

   - 12% of Na₂O;

   - 5.9% of Al₂O₃;

   and a glass composition (B) consisting of, in molar percentages:

   - 63 to 76% of SiO₂;

   - 5 to 12% of ZrO₂;

   - 0 to 12% of B₂O₃;

   - 0 to 2% of La₂O₃;

   - 11 to 14% of Na₂O;

   - 3 to 5% of K₂O.
2. The glass composition according to claim 1 which at the end of its elaboration and before any heat treatment only consists of a glassy phase.
3. The glass composition according to claim 1, comprising less than 50% by weight of crystalline phase and preferably 0% by weight of crystalline phase, after its maintaining at a temperature from 600°C to 1,000°C, notably from 700 to 900°C for a duration of more than 1 hour.
4. The composition according to any one of claims 1 and 3, wherein the composition is a visco-plastic composition and has a viscosity in the range from 10⁷ to 10⁸ dPa.s in the range from 700°C to 900°C.
5. The composition according to any one of claims 1 to 4, wherein the glass transition temperature of composition (A) is from 580°C to 620°C, and the glass transition temperature of composition (B) is from 600°C to 680°C.
6. The composition according to any one of claims 1 to 5 wherein the composition « B » consists of, in molar percentages:

   - 66% of SiO₂;

   - 5.1% of B₂O₃;

   - 13.4% of Na₂O;

   - 4.4% of K₂O;

   - 10.1% of ZrO₂;

   - 1% of La₂O₃

   or else by:

   - 74.9% of SiO₂;

   - 12.9% of Na₂O;

   - 4.2% of K₂O

   - 7% of ZrO₂;

   - 1% of La₂O₃.
7. The glass composition according to any one of claims 1 to 6, which appears in the form of a powder or else of a solid block.
8. A method for assembling at least two parts, wherein the following successive steps are carried out:

   - the parts are put into contact with a glass composition according to any one of claims 1 to 7;

   - the assembly formed by the parts and the glass composition is heated to a temperature that is sufficient to melt the glass composition so as to form a gasket between the parts;

   - the assembly formed by the parts and the gasket is cooled.
9. The method according to claim 8, wherein the step of putting the parts into contact with the glass composition is carried out by forming a powder of the glass composition, by suspending this powder in an organic binder so as to obtain a suspension or slurry, paste, and by coating at least one surface of the parts to be assembled with the obtained suspension or slurry, paste.
10. The method according to claim 8, wherein the step of putting the parts into contact with the glass composition is achieved by preparing a glass part having the shape of the gasket to be formed and then by placing this part between the surfaces of the parts to be assembled.
11. The method according to claim 10, wherein said glass part is prepared by compacting and then sintering a powder of the glass composition in a mold compliant with the shape of the glass part.
12. The method according to claim 10, wherein said glass part is a solid glass block prepared by direct casting of the molten glass composition into a mold compliant with the shape of the glass part.
13. The method according to any one of claims 8 to 12, wherein the parts to be assembled are made of a material selected from metals; metal alloys; ceramics; and composite materials comprising several of the aforementioned materials.
14. The method according to any one of claims 8 to 13 wherein said at least two parts to be assembled are made of different materials.
15. The method according to any one of claims 8 to 14, wherein said at least two parts to be assembled are parts of a high temperature electrolyzer HTE or of a high temperature fuel cell SOFC.
16. A gasket obtainable by the method according to any one of claims 8 to 15.
17. An assembly obtainable by the method according to any one of claims 8 to 15.
18. A high temperature electrolyzer or high temperature fuel cell comprising an assembly according to claim 17.

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